OP0173 CHARACTERIZATION OF AXIAL INVOLVEMENT USING 18F-FLUORIDE PET-CT IN SPONDYLOARTHRITIS PATIENTS
Authors: I. Giovannini, A. Zabotti, S. Diodato, C. Cicciò, M. Salgarello, D. Mcgonagle, I. Tinazzi
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Nuclear medicine positron emission tomography (PET) has limited evidence in the clinical management of axial Spondylarthritis (AxSpA). The 18F-fluoride isotope is a bone-specific tracer that is incorporated in the skeleton during bone remodelling. Osteoblastic bone remodeling, that culminates in new bone formation in SpA can be molecularly imaged with 18F PET. Although not widely employed, several studies have shown that 18F is an excellent isotope for evaluating sites of active osteoblastic activity<sup>[1]</sup>, and may be used in the assessment of axial involvement in spondyloarthritis<sup>[2]</sup>. <h3>Objectives</h3> Aim of this study is to identify the pattern of distribution of 18F uptake at baseline using the PET-Computerized Tomography (PET-CT) in the early AxSpA identification in patients with inflammatory back pain (IBP) according to ASAS criteria<sup>[3]</sup>. <h3>Methods</h3> We analyzed data of 18F PET-CT in patients presenting IBP suspicious for SpA. Patients were assessed clinically at baseline and according to clinical practice with assignment of a the final diagnosis of axial SpA after at least two years of follow up, according to the ASAS criteria<sup>[4]</sup>. We evaluated the baseline 18F PET-CT abnormalities and correlated with the final diagnosis. <h3>Results</h3> 125 patients underwent 18F PET-CT. 83 were female (66,4%), and the mean age at evaluation time was 49.58 years (SD 11.03). Patients were classified into 5 groups according to the rheumatological diagnosis made after at least 2 years of follow-up. Ten patients fulfilled New York criteria for Ankylosing Spondylitis (AS), 28 patients fulfilled CASPAR criteria for Psoriatic Arthritis (PsA), 35 patients fulfilled ASAS criteria for undifferentiated SpA, and 12 patients presented axial-SpA related IBD. 40 patients were not classifiable as AxSpA (not-class AxSpA). The prevalence of 18F PET-CT abnormalities highlight differences in SpA phenotypes, shown in colour coding (Figure 1A). Similar results were reported in the chest, in particular among the sterno-clavicular and acromio-clavicular joints (Figure 1B). <h3>Conclusion</h3> Our study showed a clear pattern of abnormalities detected by 18F PET-CT in the spine and chest of AxSpA patients. 18F PET-CT might help clinicians to characterize the axial involvement in SpA patients. <h3>References</h3> [1] Raynor W et al, <i>Curr Osteoporos Rep</i>. 2016;14:115-125. [2] Idolazzi L et al, <i>Ann Nucl Med</i>. 2016;30:430-434. [3] Sieper J et al, <i>Ann Rheum Dis</i>. 2009;68:784-788. [4] Rudwaleit M et al, <i>Ann Rheum Dis</i>. 2009;68:770-776. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Ivan Giovannini Speakers bureau: not relevant for this type of study, Alen Zabotti Speakers bureau: not relevant for this type of study, Stefania Diodato: None declared, Carmelo Cicciò: None declared, Matteo Salgarello: None declared, Dennis McGonagle Speakers bureau: not relevant for this type of study, Consultant of: not relevant for this type of study, Ilaria Tinazzi Speakers bureau: not relevant for this type of study.